Mobile cellular to satellite telecommunication systems, and in particular the installation, programming and accessing of subscriber interface modules thereof.
Mobile cellular to satellite communication, or SatCom, system radio transceivers having multiple voice and data input/output channels are known. Such mobile cellular to SatCom systems accept data and voice from various sources onboard a host aircraft or other vehicle, encode and modulate this information to appropriate Radio Frequency (RF) carrier frequencies, and transmit these carriers to a satellite constellation for relay to the ground. Mobile cellular to SatCom systems also receive RF signals from the satellite constellation, demodulate these signals, perform the necessary decoding of the encoded messages, and output data or voice for use onboard the aircraft by crew members and passengers. One example of such a mobile cellular to SatCom system is the AIRSAT(copyright) Multi-Channel Satellite Communication System, described in a brochure published October 1997 by AlliedSignal Incorporated, entitled xe2x80x9cAIRSAT MULTI-CHANNEL SATELLITE COMMUNICATION SYSTEM for IRIDIUM(copyright),xe2x80x9d which provides worldwide continuous multichannel voice and data communications for commercial air transport aircraft.
While the number of communication channels provided depends upon the manufacturer""s implementation, a typical mobile cellular to SatCom system unit supports multiple communication channels. One specific implementation currently provides 30 voice channels and 30 data channels. Specific proprietary implementations of the mobile cellular to SatCom system unit support multiple external interfaces, including, for example, up to 30 digitized voice channels interfacing with user terminals. Onboard a host aircraft the user terminals are the cabin and passenger telecommunication equipment, such as seatback telephone handsets. The user terminals interface with the mobile cellular unit control system through Subscriber Interface Modules, or SIM cards, that hold the user""s identification for billing and other purposes. The SIM cards also each convert analog voice input into a digitized serial data stream. Multiple SIM cards are associated with each channel of the mobile cellular unit. The SIM cards, sometimes referred to as microprocessor cards, include an eight-bit microprocessor that ensures the safety of the data and allows multiple use of a single user terminal.
All mobile cellular units use a micro-controller, or microprocessor, to interface between the main system central processing unit, or CPU, and the SIM cards. The micro-controller is part of a SIM card reader, which also includes several interface circuits, one for each SIM card. The main CPU lacks the processing time available to handle the actual serial data. The SIM card reader off-loads processing overhead from the main system CPU and relays information from the SIM cards. Although all known SIM card readers include a micro-controller interface between the main system CPU and the SIM interface circuits, the SIM card reader generally allows the micro-controller access to only one or at most two SIM cards.
One known implementation includes multiple conventional universal asynchronous receiver-transmitters, or UARTs, each interfacing with a each SIM card to convert the SIM card serial output to parallel data so that it can be received by the CPU. Another known implementation includes a conventional UART and a micro-controller to interface between the SIM cards and the CPU, but fails to allow access to more than one SIM card. Still another known implementation includes a conventional universal asynchronous receiver-transmitter, or UART, to manage the serial output of the micro-controller for the CPU. Although this combination of micro-controller and UART in the SIM card reader allows the main system CPU to access up to six to nine SIM cards, even this level of access is insufficient in mobile cellular units providing as many as 30 or more voice channels. A mobile cellular unit would require several of any of the prior art SIM card readers to support such a large number of channels, thus resulting in multiples of the SIM card reader functionality. Furthermore, the additional micro-controllers reduce overall system reliability.
FIG. 1 is a block diagram of one prior art mobile cellular unit 5 transmitting and receiving signals between multiple user terminals, such as cabin and passenger telecommunication equipment onboard a host aircraft or other vehicle, for example, seatback telephone handsets, and a satellite constellation for relay to ground stations. The mobile cellular unit must access each of the user terminals to provide this user terminal-to-satellite interface. As shown in FIG. 1, the mobile cellular unit of the prior art includes a control system 100 having a main system central processing unit, or CPU, 110 performing the actual receive and transmit functions between mobile cellular unit 10 and the satellite constellation. CPU 110 interfaces with multiple user terminals through a SIM card reader 112.
The SIM card reader illustrated in FIG. 1 is the only known prior art device that permits the main system CPU to access more than one or two SIM cards. Other mobile cellular units require a different SIM card reader to access each SIM card. In FIG. 1, prior art SIM card reader 112 includes a built-in microprocessor, or micro-controller, 114 coupled via common serial I/O chip select. The chip select is a common control line available on each discrete SIM interface module or circuit 116. An active SIM interface circuit 116 has sole ownership of the common serial I/O line. Multiple lines CS1, CS2 through CSN couple to up to nine separate and independent interface circuits 116 to common serial I/O of micro-controller 114. Thus, each interface circuit 116 allows micro-controller 114 to access one Subscriber Interface Module, or SIM card, 118. SIM cards 118 interface with the user terminals to convert analog voice input into a digitized serial data stream for transmission over the serial interface to micro-controller 114. Micro-controller 114 off-loads control of individual SIM cards 118 from main system CPU 110, thereby reducing demands on the processing time required to handle the actual serial data. Micro-controller 114 incorporates an address register that it decodes to obtain chip selects for SIM cards 118. These chip selects are used by SIM card interface circuits 116 to access individual SIM cards 118.
Micro-controller 114 relays information from SIM cards 118 to CPU 110 over a standard RS232 interface. SIM card reader 112 also. includes a universal asynchronous receiver-transmitter, or UART, 120 at each end of the RS232 interface to manage the serial output of micro-controller 114 for CPU 110 by converting the serial data to parallel data so that it can be received by CPU 110. Still, mobile cellular unit requires multiple SIM card readers 112 to an nine SIM cards, such as is presented by one or more current mobile cellular-to-SatCom implemetations. Thus, as shown, the prior art device requires a complexity and redundancy of circuitry that increases the device cost while reducing reliability.
Accurate mapping of SIM cards to their associated terminals in the mobile cellular unit is critical to functionally enabling a system for operation on the mobile cellular to SatCom network. In a typical installation, the SIM cards are installed in the field. The field installer is required to accurately record each SIM card identification number and note the installation slot to which the SIM card applies. For aircraft installations which incorporate multiple SIM cards for handling multiple user terminals, the field installation process provides numerous opportunities for documenting and recording errors. For example, SIM card identification number transposing, mis-entering and/or mis-recording during installation of the physical slot location in which each individual SIM card resides within the mobile cellular unit.
Furthermore, field installation of SIM cards eliminates the opportunity for operational verification of the SIM card-to-control system electronic interface prior to installation. Field installation also introduces the potential for contamination of the SIM card""s electrical contacts and subsequent degradation in operational reliability.
What is needed to ensure operationally integrity of the mobile cellular unit is an accurate and verifiable method of installing and mapping the SIM cards to associated terminals in the control system and a simplified physical construction with less operational components. For example, due to the safety rating of certain satellite communication products, it is undesirable to have field installation of SIM cards and additional processors in the mobile cellular unit.
The present invention overcomes the method and device limitations of the prior art by providing an interface circuit for use in a mobile cellular to satellite telecommunication system for interfacing between a main system central processing unit and multiple communication channels whereby the prior need for a micro-controller is eliminated. The present invention provides an enhanced UART interface circuit incorporating the functions of the micro-controller of the prior art, thereby eliminating the need for a micro-controller and simultaneously simplifying the device and the method.
According to one aspect of the invention, the UART interface circuit includes a receive function adapted to receive serial data through a standard serial I/O port from individual ones of the multiple communication channels of a mobile cellular to satellite telecommunication system; a control function cooperating with the receive function and adapted to control access to individual ones of the multiple communication channels; and a transmit function cooperating with each of the receive function and the control function, the transmit function adapted to transmit parallel data through a standard parallel port to the main system central processing unit. According to various aspects of the invention, the control function includes multiple control registers converting the serial data character stream received from the communication channel into parallel data; multiple data lines transferring each serial data character and for reading and writing to the control registers; multiple address lines, controlling which of the multiple control registers is accessed; and a chip select determining which one of the multiple communication channels is accessed.
According to another aspect of the invention, the receive function is further adapted to receive parallel data from the main system central processing unit of the mobile cellular to satellite telecommunication system, perform serial-to-parallel data conversion on the received parallel data, and the transmit function is further adapted to transmit the resulting serial data to predetermined ones of the multiple communication channels.
According to another aspect of the invention, the control function further includes an extra guard time counter for timing extra guard time for the multiple communication channels of the mobile cellular to satellite telecommunication system. Preferably, the extra guard time counter is implemented in hardware.
According to other aspects of the invention, receive function further includes an error detection function, which detects parity errors and asserts an error signal/retransmit request signal in response to a detected parity error. The transmit function further includes a detection function coupled to the receive function, which detects an asserted error signal/retransmit request signal.
Preferably, the detection function retransmits the last of the data characters in response to a detected error signal/retransmit request and generates an interrupt signal indicating the end of the retransmission of the last data characters in response to a signal received from the extra guard time counter indicating that the extra guard time has expired.
According to still another aspect of the invention, the present invention provides a method for interfacing between a system central processing unit and multiple communication channels, which eliminates the micro-controller of the prior art, thereby simplifying the process and improving reliability of control. According to the invention, the method for interfacing between a system central processing unit and multiple communication channels includes determining which individual one of the multiple communication channels is accessed; receiving a stream of serial data characters from the accessed communication channel; translating or converting the serial data characters into parallel data words; and transmitting the resulting parallel data words to the main system central processing unit.
According to another aspect of the invention, the method of receiving the serial data stream also includes detecting any parity errors in the serial data and asserting an error signal/retransmit request signal if a parity error is detected. Preferably the method further includes re-transmitting the last data character in response to an asserted error signal/retransmit request signal, and then generating an interrupt signal indicating the end of the retransmission. Preferably, generation of the interrupt signal is further dependent upon receiving a signal indicating the end of an extra guard time period.
According to yet another aspect of the invention, the invention provides a mobile cellular to satellite telecommunication system in which the micro-controller of the prior art is eliminated and an enhanced UART circuit assumes the function of performing serial data protocols and error checking. The mobile cellular to satellite telecommunication system of the invention includes multiple Subscriber Interface Modules, or SIM cards, that hold the user""s identification for billing and other purposes and multiple SIM card interface circuits coupling individual SIM cards to the enhanced UART circuit of the invention, which performs the necessary serial data protocols and error checking. The enhanced UART circuit of the invention is coupled to the parallel port of a main system CPU, which receives the converted parallel data.
According to anther aspect of the invention, the enhanced UART circuit of the invention includes a chip select for addressing different individual ones of the SIM cards; multiple data lines for transferring the serial data characters received from the SIM card interface circuits and for reading and writing to different ones of a quantity of control registers; and an address register which is decoded by the SIM card interface circuits to obtain different chip selects, the address register corresponding to a quantity of address lines that determine which of the many control registers is accessed.
According to different aspects of the invention, the enhanced UART circuit of the invention is either embedded in a interface circuit coupled to a parallel port of the CPU, or embedded in a separate hardware module coupled to a parallel port of the CPU.
Other aspects of the invention also provide a method for controlling a mobile cellular to satellite telecommunication system, without the micro-controller of the prior art. The method of the present invention includes accessing an individual one of multiple communication channels, and through that channel accessing an individual one of multiple SIM cards; receiving a stream of serial data characters from the accessed communication channel; converting, or translating, the received serial data characters into parallel data words; and transmitting the resulting parallel data character words to the main system central processing unit.
According to aspects of the invention, preferred embodiments of the method of the invention include a receiving further detecting parity errors in the received serial data and asserting an error signal/retransmit request signal when a parity errors is detected. Preferably, the method also includes re-transmitting the last one of the data characters in the data stream when an asserted error signal/retransmit request signal is generated and received. Preferred embodiments of the invention also generate an interrupt signal indicating the end of the data character retransmission.
According to still other aspects of the invention, the method further provides remotely installing one or more of the SIM cards into a hardware carrier, for example, in the OEM factory, each SIM card forming multiple electrical interfaces with the hardware carrier; testing each SIM card-to-hardware carrier electrical interfaces; identifying each SIM card position in the hardware carrier and cross-referencing the SIM card position against a part number and serial number assigned to that hardware carrier; recording the information, preferably in electronic form downloaded to a computer diskette or an accessible network file; and installing the SIM cards in the hardware carrier into the mobile cellular to satellite telecommunication system.
According to preferred aspects of the invention, the recorded information is transferred to a customer support function, such as a customer support center supporting the installation function. Preferably, at the time of installation, the installer reports the part number and serial number assigned to the hardware carrier to the customer support group. Preferably, the customer support function locates the record using the part number and serial number information and activates the SIM cards for use in the mobile cellular to satellite telecommunication system.